I'm writing this post to highlight a problem I've encountered with User Defined Routes/Route Tables, and their implementation on Azure Stack. I'll not go into detail on when to use UDR's; the official documentation does a great job of that: https://docs.microsoft.com/en-us/azure/virtual-network/virtual-networks-udr-overview#custom-routes

Typically you would use a UDR within an Azure Stack tenant's VNet when you want to direct internet bound traffic via a third party network virtualized appliance (e.g. Firewall).

Azure Stack offers the ability to add Public IP Pools should the one you provided when the installation took place not be sufficient for your needs going forward.  Typically this will be the case when an operator starts to receive alerts in the Admin portal like this:

OK, so this may be an intermittent warning, happening once every so often.  If so, I suggest there's no need to take any action.  However, if you get an alert warning of 90% utilization across all pools, it's time to take action, and that is to look into adding an extra pool.